The television signals originating from a satellite are amplified and converted into a predetermined frequency band, typically 950 MHZ to 2,150 MHZ, by way of a parabolic dish and a low-noise converter located at the focus of the parabolic dish. This signal is then dispatched to the input of the tuner of the receiver. The purpose of the tuner is to select the desired channel and to output a baseband signal on the in-phase path (I path) and on the quadrature path (Q path). This signal is then converted into a digital signal and demodulated.
The channel decoding processing also comprises a block which distinguishes the zeros from the ones, typically by means of majority logic, then performs the entire error correction. Error correction may typically be Viterbi decoding, deinterlacing, Reed-Solomon decoding and deshuffling. The channel decoding device outputs packets which are decoded in a conventional manner in a source decoding device in accordance with the MPEG standards to redeliver at the output, the initial audio and video signals transmitted via the satellite.
At the input of the receiver, the signal received is composed of the collection of channels which are transmitted from the satellite and are transposed into the 950 MHZ to 2,150 MHZ frequency band. The overall power received is substantially equal to the mean power on a channel increased by ten times the Napierian logarithm of the number of channels. This signal possesses a considerable variation on the order of 50 dBm.
At present, in receivers as a whole, the signal received at the input is normally filtered by a wide band type filter, whose passband is on the order of several hundred MHZ, which is placed just after the low-noise input amplifier. This is done to avoid the saturation of the subsequent stages of the tuner, especially the controlled-gain amplification stages as well as the mixers of the frequency transposition stage.
Furthermore, current approaches provide for the low-noise input amplifier and the wide band filters to be made external from the chip containing the controlled-gain amplifying stage as well as the frequency transposition stage. These filters, whose cut-off frequencies can be tailored by selecting the desired channel, are then embodied as discrete components, such as varicap diodes. Such components, are of an overly large size which is incompatible with a fully integrated embodiment of the tuner.